This invention relates to electrical assemblies and to drive means for a movable structure therein. The invention is particularly applicable to low voltage distribution and supply networks incorporating fuse and/or switch means.
In the particular context of low voltage supply distribution from indoor and outdoor sub-stations the network incorporates a fuse board, fuse pillar or fuse cabinet as appropriate to the particular environment. Conventionally, four or five supply bus bars are provided, one for each of the three phases and either a common neutral/earth bar or separate neutral and earth bars. Each three-phase output taken from the supply has each power-carrying cable connected to the bus bar of the respective phase by way of a fuse, the three fuses being mounted together on a distributor unit. Each fuse is designed to engage and bridge two spaced contacts, one electrically connected to the respective bus bar, and the other to the respective output.
In distribution arrangements of this type manufactured to conform to the requirements of the British Electricity Supply Industry Standard, each pair of fuse contacts is fully exposed when not bridged by their associated fuse. The contacts are bridged by engaging the fuse with one of the contacts and, pivoting about the point of engagement, driving the fuse manually into engagement with the other contact. A fuse holder may be permanently or detachably connected to the fuse, the operator then grasping the fuse holder rather than the fuse itself. Speed and firmness are necessary if safe fuse insertion is to be achieved when the bus bar is live. This is particularly so if there should be a fault condition on the output line, as severe arcing is liable to take place, with consequent hazard to the operator. Removal of a fuse from a live circuit requires a similar firmness of action and can again be dangerous. These hazards of operation, coupled with the exposure of potentially live contacts when fuses are not present render this type of distribution equipment dangerous.
On the continent of Europe equivalent distribution equipment does provide for shrouding of the contacts when the fuse is not in position, and also includes shrouding to direct arcing away from an operator inserting or removing the fuse, and means to assist in quenching arcs. Nevertheless, there is potential danger, and safe operation still depends on the speed and firmness of the operator while manually removing or inserting fuses.
In other types of distribution equipment insertion and removal of fuses may be assisted by a mechanism permanently associated with each fuse and controllable to effect the necessary operation. Although providing increased operator safety such equipment is expensive.
The present invention seeks to improve the safety and economy of distribution assemblies as aforesaid, and is also applicable to the operation of fuses and/or switches in other types of electrical assembly.